This invention relates to a color video camera system that can be utilized for motion picture film origination, and also relates to an optical prefiltering method and apparatus that can be used in conjunction with a color video camera system.
Color motion pictures are often made by shooting the action with a film camera, converting the images to digital form, computer processing the digital images, and then scanning the processed images back onto film for release. It would be advantageous to have a practical electronic color video camera that could directly shoot the action to obtain color video from which good quality color motion picture film could ultimately be produced, but this has not yet been achieved. A major reason is that the expensive high quality lenses used in motion picture film cameras have optical characteristics and requirements that are not readily adaptable to electronic video cameras. A 24 frames per second progressively scanned color video camera for electronic film origination has become available. It is a three-sensor camera that must use lenses designed for television cameras, and cannot achieve the image quality that is obtainable with the high quality lenses used in motion picture film cameras.
It is among the objects of the present invention to devise an electronic color video camera that can utilize the types of high quality lenses that are used in motion picture color film cameras. It is also among the objects of the present invention to provide an improved beamsplitter and optical prefilter for use in electronic color video cameras.
In a form of the parent application hereof, there is set forth a technique for producing electronic video signals representative of color images of a scene, comprising the following steps: providing a luminance sensor and a color sensor having a color filter thereover; providing a beamsplitter, and providing a motion picture film camera type of lens system that focuses light from the image, via the beamsplitter, onto the luminance sensor and the color sensor; and producing electronic video signals from outputs of the luminance sensor and the color sensor. In one embodiment of the invention in the parent application, the step of providing a beamsplitter comprises providing a pellicle beamsplitter. In another embodiment thereof, a rotating shutter/mirror is used as a temporal beamsplitter. In an embodiment of the present invention, the shutter/mirror is also utilized to a achieve optical prefiltering, this being achieved by introducing a controlled wobble of the image reflected toward the color sensor.
In accordance with an embodiment of the present invention, there is set forth a method for producing electronic video signals representative of color images of a scene, comprising the following steps: providing a luminance sensor and a color sensor having a color filter thereover; providing a temporal beamsplitter, and providing a lens system that focuses light from the image, via the beamsplitter, alternately onto the luminance sensor and the color sensor; and producing electronic video signals from outputs of the luminance sensor and the color sensor; the step of providing a temporal beamsplitter comprising providing a rotating mechanical shutter that includes an open sector that passes light from the image toward the luminance sensor and a mirrored sector that reflects light from the image toward the color sensor in the path of light from the image, and rotating the shutter in a manner to cause a wobble of the image on the color sensor.
In a preferred embodiment of the invention, the step of rotating the shutter includes mounting the shutter on a shaft such that the shutter is offset from the normal to the shaft by an angle that causes the wobble. In this embodiment, the angle is preferably in the range between 1 second of arc and 1 degree of arc. Also, in a preferred embodiment, the color sensor has a characteristic pixel spacing, and the excursion of the image on said color sensor due to said wobble is at least half the pixel spacing.
Further features and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.